1. Field of the Invention
The present invention relates generally to how to lubricate a linear transmission device, and more particularly, to a lubrication monitoring system for a linear transmission device.
2. Description of the Related Art
U.S. Pat. No. 6,179,597 disclosed an automatic lubricator for an injection molding machine, characterized in that a lubrication interval Ls of the automatic lubricator is controlled according to length of cycle time S of the injection molding machine. When the cycle time S is longer, the lubrication interval Ls is relatively increased. When the cycle time S is shorter, the lubrication interval Ls is relatively decreased. Besides, the change of temperature is also listed in the conditions as to whether the lubrication is needed or not.
The aforesaid lubrication approach judges whether to lubricate based on the cycle time and the temperature and then lubricates at a predetermined time without considering the actual lubricative state of the linear transmission device. In this way, when the cycle time S is erroneously judged, it may happen that the lubrication is applied when it is not needed or the lubrication is not applied when it is needed.
In addition, PCT Pat. Pub. No. WO 2008/093652 disclosed a lubricative state detector and lubricative state detecting method, in which an electric resistance value detected while the lubrication is sufficient is acted as a threshold preset and a detected electric resistance between the tracker member and the moving block is compared with the threshold preset to judge whether it is necessary to resupply the lubricant according to the current lubricative state.
As indicated above, the aforesaid PCT patent is to compare the electric resistance values under the operation of the linear transmission device. Because the horizontal axis in operation is isokinetically less loaded to have smaller electric resistance value, it cannot indicate that the lubrication is insufficient. For this reason, whether such lubricative state is correct or not is still questionable.